The Science Behind James Cameron's Avatar

In Cameron's movie, Alpha Centauri's glow lights up the giant gaseous planet Polyphemus and its tropical moon Pandora. But how accurate is that depiction? (MSX/IPAC/NASA)

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In Cameron's movie Avatar, men work, combat and stomp through Pandora's rainforest in armored exoskeletal vehicles. But how realistic is that? (20th Century Fox)

It's the year 2154 and humankind has reached out to the stars in director James Cameron's new science-fiction epic Avatar. The movie takes us to an exotic jungle moon called Pandora where humans are the aliens and a clash is brewing with the natives.

Cameron, who has served as an adviser to NASA to investigate a camera for a Mars mission, is known for taking the science in his flicks very seriously. So how did he do? Here we check on some of the movie's scientific bona fides with top researchers in their respective fields to see where artistic license and scientific plausibility meld.

In Avatar: For work, combat and stomping through Pandora's rainforest, humans gear up in Amplified Mobility Platform (AMP) suits. These armored exoskeletal vehicles are very similar to the Armored Personnel Units featured in The Matrix Revolutions and the power loader in Cameron's own Aliens, but with an enclosed cockpit.

From this perch in the machine, the movements of a human operator's arms and legs are translated to the suit's exterior limbs and "amplified." The operator swings his arm several inches, and the AMP's corresponding giant metal arm scythes a 10-foot arc.

"The super hydraulics are all very strong so [the AMP suit] can crush buildings and do all the things that, like, a tank could do," says Avatar vehicle designer Ty Ruben Ellingson in a promotional video. The Herculean strength granted to the AMP suit's operator lets space marines tote giant 30-mm autocannons into battle as easily as one might carry a rifle. In further characterizing the AMP suit, John Rosengrant, design supervisor for Stan Winston Studios, says it's "an Apache helicopter with legs."

The Science: For decades, the U.S. military has been looking into powered exoskeleton suits that could let soldiers lug around heavy equipment—as well as bigger guns—while aiding in rescue work, construction and injury rehabilitation.

The Army's research and development branch, DARPA (Defense Advanced Research Projects Agency) issued various grants since 2000 under its Exoskeletons for Human Performance Augmentation program, including funding for the Raytheon Sarcos team. Their machine, called XOS, weighs 150 pounds and fits around the wearer's arms, legs and back.

This aluminum robot's hydraulics allow the wearer to lift 200 pounds hundreds of times without tiring, yet the XOS suit remains nimble enough to allow the man-cum-machine to climb stairs or kick a soccer ball. The key hurdle for the Raytheon Sarcos device is independently powering it. For now, the XOS remains tethered to an external power source.

Other groups at MIT, Berkeley and Honda are also devising similar machines for the lower body. Meanwhile, Japanese researchers at a company called CYBERDYNE (a name shared by the fictional firm that creates Skynet in Cameron's Terminator franchise) have invented an Iron Man-style body cladding that aids in physical therapy, and is christened Robot Suit Hybrid Assistive Limb (HAL).

"Movies like Avatar are good to get us thinking about the possibilities," says David Audet, leader of the Soldier Mobility and Mission Enhancement Team at the Natick Soldier Research Development and Engineering Center in Massachusetts that has a point role in developing XOS. And while there is "a lot of Hollywood going on" with the AMP suit, it suggests the immense logistical work that such devices could render and serves as, Audet says, "an example of a foundational platform that with very little modifications can perform a large suite of attacks."

Alpha Centauri

In Avatar:The white-yellow glow of Alpha Centauri A, a star very similar to our Sun, illuminates the giant gaseous planet Polyphemus and its tropical moon Pandora. On this lush world, great beasts roam the jungles and pterodactyl-like creatures soar through the sky. A sentient, blue-skinned humanoid species known as the Na'vi has evolved here and learned to live in harmony with nature.

The Science: Alpha Centauri A is one of the three stars that make up Alpha Centauri, which is located 4.37 light years away, making it our solar system's closest stellar neighbor. This proximity has inspired an intense hunt to reveal the exoplanets that could be right next door.

Last January, a team led by Yale astronomer Barbara Fischer began a five-year survey of Alpha Centauri using a 1.5-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile. Her group is looking for rhythmic, telltale patterns in the wavelengths of a star's light caused by the gravitational tugging of orbiting worlds.

This "wobble technique" has already ruled out the presence of Jupiter- or Saturn-scale exoplanets (like Polyphemus) around the Alpha Centauri stars. But "there's a very good chance," Fischer says, that planets with masses near that of Earth's could grace this star system. "There's still so much we don't understand about planet formation around single stars," Fischer says—let alone triple-star systems like Alpha Centauri. So in terms of what may be out there, "it's almost an open slate."

The orbital mechanics of the two stars at Alpha Centauri's heart, often called Cen A and Cen B, indicate where planets are likely to reside. The stellar duo gravitationally tangos as close as 11 astronomical units (AUs, the average distance from the Sun to Earth) to each other before swinging as far apart as 36 AU. (The third star, a red dwarf called Proxima Centauri, circles this couple at a considerable distance and is too faint for Fischer's team to study, but it could boast small planets, too.)

Given this setup, the orbits of exoplanets that formed 2 AU away and more from Cen A and Cen B would get destabilized by the other star and eventually get shot right out of the system, Fischer says.

Fortunately, if life has taken root in the Alpha Centauri system, it is not likely to suffer this fate. The habitable Goldilocks zone—the not-too-hot, not-too-cold orbital band where water can be liquid on a planet or a moon's surface—is situated closer to both Cen A and Cen B. The former, a bit bigger than the Sun, has a Goldilocks zone of around 1.2 AUs out.

From Cen B, at about 90 percent of the Sun's mass, this zone is found at about 0.75 AU. Since both stars are chemically similar to the Sun, the same general mixture of elements that allowed life to develop on Earth should have been available in the primordial soups of both Cen A and Cen B's planetary brood.

For now, the jury is still out on whether the Alpha Centauri system has smaller, Earth-like worlds in life-friendly regions, but Fischer expects answers shortly. "By the end of year four [2012], we'll really know," she says. Meanwhile, other efforts led by famed planet-hunter Michel Mayor of the University of Geneva and a new initiative by the University of Canterbury in the United Kingdom may render the verdict even sooner.

For more on the science facts and science fiction in Avatar, read the full story on Popular Mechanics.